Because of the need to eliminate the hazards associated with the application of toxic chemicals such as pesticides and herbicides, chemical industry in general and the agricultural chemicals industry in particular have developed closed systems for shipping, transferring and applying chemicals. Typical of agrichemical systems are those described in U.S. Pat. Nos. 3,976,087 to Bolton et al. and 4,254,805 to Reeder. In these systems liquid chemical from a closed feed tank is delivered by vacuum to a holding tank for mixing or diluting or for measurement of desired volumes, the chemical then being transferred by suitable lines to spray applicator apparatus in aircraft.
As shown in the Reeder patent, chemical concentrate in a supply tank is transferred by vacuum through a probe having its tip disposed below the surface of the liquid chemical to a plurality of holding tanks wherein the chemical is appropriately diluted with water for subsequent delivery to spraying apparatus such as may be contained in aircraft. The line from the probe has a conventional "quick connect-disconnect" fitting for convenience in securing the probe line to a movable chassis, upon which are mounted the various holding tanks and lines. The chassis provides convenience in moving the mixing system into position for operation.
Fluid measuring circuits have been devised for use in mixing measured quantities of toxic chemicals supplied from "point-of-sale" containers. In U.S. Pat. No. 3,913,606 to Andersen, for example, a supply container is provided with a ported cover effecting a fluid-tight seal between the container and a conduit to a hermetically sealed holding tank, the tank having a sight gauge to indicate the level of toxic liquid within the tank. A flush valve and conduit connected to the bottom of the tank permits discharge through a conduit to associated tanks for mixing and/or dilution, preliminary to delivery to a spray apparatus. The connections to the supply tank include a bleeder valve for entry of atmospheric pressure into the container as and when desired. A preferred form of valve includes a ball float. The cover of the chemical supply tank is provided with a sleeve around a probe tube for fluidtight coupling of the probe tube conduit between the supply container and the holding tank.
Despite advances in closed container chemical applicator systems, including apparatus and valving design as described, for example, in the foregoing patents and U.S. Pat. Nos. 3,640,319 to Hougen and 3,916,924 to McGowen, considerable risk has persisted due, in part, to use of disposable chemical supply containers or containers designed for cleaning and refill at the application site. Such container and applicator systems, even when intended for closed system use in accordance with governmental regulations, in reality have not satisfied the needs of industry.